Technical Abstract:
Corn fiber produced from wet milling has potential as a feedstock for ethanol fermentation because of its high carbohydrate content, proximity to existing ethanol facilities, and low-cost. Most of the corn fiber xylan can be easily released from the fiber by just treating with hot-water. However, fermentation of the resulting hydrolysate is problematic because the yields of simple sugars following saccharification with commercial xylanase preparations are low. To develop more effective enzyme mixtures, both Trichoderma reesei RutC30 and Aspergillus niger strains were cultured on partially destarched corn fiber (DSCF) to induce the production of xylanolytic enzyme mixtures. The DSCF was either treated with hot-water (160 deg C for 20 min) or left untreated. Enzyme preparations were prepared from the recovered culture liquid. Xylanase activity was increased 39-150% for cultures grown on the hot-water vs. untreated DSCF. Also, as expected, T. reesei produced more cellulase compared to A. niger, while the latter produced more xylanase. Another significant difference was that the A. niger culture possessed ferulic acid esterase activity and the T. reesei culture did not. The enzyme preparations were next evaluated for production of free sugars from hot-water treated DSCF. Hot-water treatment alone released 12% of the maximum possible xylose and 54% of the arabinose. Adding either enzyme mixture increased the sugar yields to approx. 60% of the arabinose and 30% of the xylose. However, adding both preparations together further increased the yields of arabinose and xylose to 70% and 50%, respectively, and completely hydrolyzed the xylan. Current work is directed towards increasing this yield further by supplementing the preparations with auxiliary enzymes and towards testing the recovered sugars as a carbon source for ethanol fermentation.